Optical semiconductor module

ABSTRACT

An optical semiconductor module includes an optical semiconductor element; an optical fiber optically coupled with the semiconductor element; a base having an upper surface and a lower surface; and a package. The package has a bottom plate on which the base is mounted, a front wall having a hole through which the optical fiber is inserted, and a rear wall opposite to the front wall. The optical fiber and the optical semiconductor element are mounted on the upper surface. The base has a rear face formed on an end portion opposite to the front wall, and the rear face is positioned above the lower surface of the base.

BACKGROUND OF THE INVENTION

[0001] 1) Field of the Invention

[0002] The present invention relates to an optical semiconductor modulehaving an optical semiconductor element and an optical fiber that areused for optical communications.

[0003] 2) Description of the Related Art

[0004]FIG. 23A is a plan view of a part of a conventional semiconductorlaser diode (hereinafter, “LD”) module, and FIG. 23B is a longitudinalcross-sectional view of the part. The LD module includes a base 6 ontowhich a heat sink 3 and a carrier 5 are soldered. On the heat sink 3, anLD element 1 and a thermistor 2 are mounted, and on the carrier 5, aphoto diode (hereinafter, “PD”) element 4 is mounted. Further, a metalferrule 7 a supporting an optical fiber 7 is fixed onto the base 6 viatwo support members 6 a by YAG laser welding or with solder. The weldingpoints, in the drawings, are denoted by solid circles P_(wd). Theoptical fiber 7 is precisely aligned so as to be optically coupled witha laser beam emitted from the LD element 1, and is fixed onto thesupport member 6 a.

[0005]FIG. 24 is a longitudinal cross-sectional view of the conventionalLD module, where the base 6 is accommodated within a package 8, and isfixed onto a bottom plate 8 e of the package 8. The package 8 is sealedwith a lid 9 at the upper opening, thereby to complete the assembly ofthe LD module. A lensed fiber, one end of which being formed in aspherical or a wedged shape to serve as a lens portion, is used as theoptical fiber 7 in order to ensure a high coupling efficiency betweenthe optical fiber 7 and the laser beam emitted from the LD element 1.The other end of the optical fiber 7 is led out of the package 8 througha longitudinal hole 8 a of a snout 8 b prior to mounting of the base 6onto the bottom plate 8 e of the package 8. A portion between theoptical fiber 7 and the internal wall of the snout 8 b is hermeticallysealed with sealant S like solder or synthetic resin.

[0006] The LD module, particularly one using the lensed fiber, requiresthat the LD element 1 and the lensed fiber are coupled with an extremelyhigh precision, and that the optical fiber 7 and the support member 6 aare precisely positioned.

[0007] In the LD module shown in FIG. 24, the base 6 is directly fixedonto the bottom plate 8 e, with no Peltier module for coolinginterposed. The longitudinal hole 8 a in FIG. 24 is formed through afront wall 8 c of the package 8 at a position far down from the upperend of the front wall 8 c. Such position of the longitudinal hole 8 amakes the mounting of the base 6 difficult.

[0008]FIG. 25 is a longitudinal cross-sectional view of the conventionalLD module in the mounting step. In the mounting step, the base 6 isaccommodated onto the bottom plate 8 e, maintaining a state that theoptical fiber 7 passes through the longitudinal hole 8 a. In such asituation, a position of the metal ferrule 7 a holding the optical fiber7 is limited by the position of the longitudinal hole 8 a, causing oftenan interference between a lower portion of the base 6 and a rear wall 8d of the package 8 when mounting the base 6, depending on sizes of thepackage 8 and the base 6. And while the base 6 is being mounted onto thebottom plate 8 e of the package 8 so as to avoid the interference,stress is often applied to the optical fiber 7 and thereby the opticalfiber 7 is bent, pressed, or pulled. In this way, this stress oftencauses misalignment between the LD element 1 and the optical fiber 7.

[0009] Further, in the mounting step, the optical fiber 7 is oftenexcessively bent at a portion A encircled by a dashed line in FIG. 25,by contact with the snout 8 b. In some cases, the optical fiber 7 iscoated with metal (e.g., gold), in order to facilitate the hermeticsealing of the optical fiber 7 inside the inner space of the snout 8 bwith solder S or other sealant, or in order to facilitate the solderingof the optical fiber 7 to the base 6. Such metal-coated optical fibershave a minimum allowable bending curvature radius larger than that ofnon-coated optical fibers and are more repulsive against the bendingdeformation. Therefore, the optical fiber 7 needs to be handled so asnot to be bent too much.

[0010] The similar situation may be present not only in opticalsemiconductor modules in general of butterfly-type, including receivermodules (hereinafter, “PD modules”) having a PD element mounted on thebase 6, but also in the LD module of so-called DIL (Dual In Line) typewhich utilizes a small-sized package.

SUMMARY OF THE INVENTION

[0011] The optical semiconductor module according to one aspect of thepresent invention includes an optical semiconductor element; an opticalfiber optically coupled with the semiconductor element; a base having anupper surface and a lower surface, the optical fiber and the opticalsemiconductor element being mounted on the upper surface; and a packagehaving a bottom plate on which the base is directly mounted, a frontwall having a hole through which the optical fiber is inserted, and arear wall opposite to the front wall, wherein the base has a rear faceformed on an end portion opposite to the front wall, the rear face beingpositioned above the lower surface.

[0012] The optical semiconductor module according to another aspect ofthe present invention includes an optical semiconductor element; anoptical fiber optically coupled with the semiconductor element; a basehaving an upper surface and a lower surface, the optical fiber and theoptical semiconductor element being mounted on the upper surface; apackage having a bottom plate on which the base is directly mounted, anda front wall having a hole through which the optical fiber is inserted;and a lid having a first portion disposed above the base and a secondportion facing the hole, the first portion and the second portion of thelid being combined with each other to cover the package.

[0013] The other features and advantages of the present invention arespecifically set forth in or will become apparent from the followingdetailed descriptions of the invention when read in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1 is a longitudinal cross-sectional view of a LD moduleaccording to a first embodiment of the present invention;

[0015]FIG. 2 is a top plan view of a package of the LD module shown inFIG. 1;

[0016]FIG. 3 is a longitudinal cross-sectional view of a part of the LDmodule shown In FIG. 1;

[0017]FIG. 4 is a longitudinal cross-sectional view of the LD module inthe mounting step;

[0018]FIG. 5A and FIG. 5B are longitudinal cross-sectional views ofother examples of a base of the LD module;

[0019]FIG. 6A is a top plan view of other example of the base, and FIG.6B is a longitudinal cross-sectional view of the base shown in FIG. 6A;

[0020]FIG. 7 is a longitudinal cross-sectional view of a LD moduleaccording to one example of a second embodiment of the presentinvention;

[0021]FIG. 8 is a longitudinal cross-sectional view of the LD moduleshown in FIG. 7 in the mounting step;

[0022]FIG. 9 is a longitudinal cross-sectional view of a LD moduleaccording to another example of the second embodiment in the mountingstep;

[0023]FIG. 10 is a longitudinal cross-sectional view of a LD moduleaccording to still another example of the second embodiment in themounting step;

[0024]FIG. 11 is a longitudinal cross-sectional view of a LD moduleaccording to still another example of the second embodiment in themounting step;

[0025]FIG. 12 is a longitudinal cross-sectional view of a LD moduleaccording to still another example of the second embodiment in themounting step;

[0026]FIG. 13 is a longitudinal cross-sectional view of a PD moduleaccording to a third embodiment of the present invention;

[0027]FIG. 14A is a top plan view of one example of a base used for thePD module shown in FIG. 13, and FIG. 14B is a side view of the baseshown in FIG. 14A;

[0028]FIG. 15 is a longitudinal cross-sectional view of the PD moduleshown in FIGS. 14A and 14B in the mounting step;

[0029]FIG. 16 is a side view of a LD module according to a fourthembodiment of the present invention;

[0030]FIG. 17 is a top plan view of the LD module shown in FIG. 16;

[0031]FIG. 18 is a longitudinal cross-sectional view of a LD moduleaccording to a fifth embodiment of the present invention;

[0032]FIG. 19 is a longitudinal cross-sectional view of the LD moduleshown in FIG. 18 in the mounting step;

[0033]FIG. 20 is a longitudinal cross-sectional view of another exampleof the LD module according to the fifth embodiment, having a differentpackage from that shown in FIG. 18;

[0034]FIG. 21 is a longitudinal cross-sectional view of still anotherexample of the LD module according to the fifth embodiment, having adifferent form of a snout from that shown in FIG. 18;

[0035]FIGS. 22A to 22C are longitudinal cross-sectional views of stillother examples of the LD module according to the fifth embodiment,having different forms of a snout and different forms of a base from theLD module shown in FIG. 18;

[0036]FIG. 23A is a plan view of a part of a conventional LD module, andFIG. 23B is a side view of the part;

[0037]FIG. 24 is a longitudinal cross-sectional view of the conventionalLD module; and

[0038]FIG. 25 is a longitudinal cross-sectional view of the conventionalLD module in the mounting step.

DETAILED DESCRIPTION

[0039] Exemplary embodiments of the optical semiconductor modulerelating to the present invention will be explained in detail below withreference to the accompanying drawings. In the following embodiments,constituent parts identical with those of the LD module shown in FIG. 24are designated with like reference symbols.

[0040] An optical semiconductor module according to a first embodimentof the present invention is an LD module. FIG. 1 is a longitudinalcross-sectional view of the LD module. This LD module 10 differs fromthe conventional LD module shown in FIG. 24, in that a base 11 is fixedonto the bottom plate 8 e instead of the base 6. On the base 11 areprovided, the heat sink 3 mounting thereon the LD element 1 and thethermistor 2, the carrier 5 mounting thereon the PD element 4, and twopieces of support members 11 a supporting the metal ferrule 7 a holdingthe optical fiber 7. The metal ferrule 7 a is fixed to the base 11through the two support members 11 a by YAG laser-welding or soldering.The optical fiber 7 is arranged to pass through the longitudinal hole 8a of the snout 8 b. The portion between the optical fiber 7 and theinternal wall of the snout 8 b is hermetically sealed with a sealant Slike solder. The package 8 is sealed with the lid 9 at the upperopening. The package 8 also has a front wall 8 c and a rear wall 8 dthat faces the front wall 8 c.

[0041]FIG. 2 is a top plan view of the package 8. The package 8 is of abutterfly type having a plurality of leads L_(d) protruding from thepackage 8 at both sides. The snout 8 b is covered with a rubber coveringB_(g). A part of the optical fiber 7 that is led out of the package 8 isprotected by a protective tube T_(g). The package 8 has a length L notlarger than 16 millimeter, a width W not larger than 10 millimeter, anda height H not larger than 8 millimeter, as shown in FIGS. 1 and 2.

[0042]FIG. 3 is a longitudinal cross-sectional view of a part of the LDmodule shown in FIG. 1, and specifically illustrates the base 11. Thebase 11 differs from the base 6 shown in FIGS. 23A, 23B, 24, and 25, inthe shape of the rear end portion to be faced to the rear wall 8 d ofthe package 8. As shown in FIG. 3, the base 11 has a rear end portion Ehaving an upper edge F_(U) and an lower edge F_(L). The lower edge F_(L)is positioned nearer to the front end portion of the base 11 than theupper edge F_(U). In other words, the base 11 has a taper 11 b that isinclined from the vicinity of the upper edge F_(U) toward the lower edgeF_(L), at the rear end portion E. As a result, the formation of thetaper 11 b is equivalent to elimination of the rear lower corner of thebase 11.

[0043]FIG. 4 is a longitudinal cross-sectional view of the LD module inthe mounting step. When the base 11 is mounted into the package 8 in adirection of an arrow mark shown in the FIG. 4, no interference occursbetween the base 11 and the rear wall 8 d of the package 8. This isbecause of the elimination of the rear lower corner of the base 11 bythe taper 11 b. Therefore, the base 11 can be easily mounted onto thebottom plate 8 e of the package 8. Consequently, no significantmisalignment between the LD element 1 and the optical fiber 7 can occurin the mounting step and it is possible to suppress a reduction in thecoupling efficiency between the laser beam emitted from the LD element 1and the optical fiber 7.

[0044] Moreover, the prevention of interference between the base 11 andthe rear wall 8 d results in a prevention of an excessive bend of theoptical fiber 7 at the portion A encircled by the dashed line in FIG. 4.Consequently, the optical fiber 7 can be maintained at a large radius ofbending curvature during the mounting step into the package 8, and isfree from a breakage arising from the excessive bending.

[0045] The shape of the rear end portion E of the base 11 is not limitedto that shown in FIG. 3. The rear end portion E may be formed intovarious shapes to avoid an interference against the rear wall 8 d in themounting step. For example, the rear end portion may be formed into acurved face 11 c with a curvature radius of r as shown in FIG. 5A, or astep 11 d with a height h2 and a length L1 as shown in FIG. 5B.

[0046] In the LD module 10 according to the present embodiment, the base11 is mounted into the package 8 in the state that the rear end portionE is slightly inclined from a horizontal state such that the opticalfiber 7 led from the snout 8 b to the outside of the package is notexcessively bent. When the base 11 is formed Into the taper 11 b, forexample, a height h1 of the base 11 from its bottom surface to a line ofintersection between the taper 11 b and the rear end surface of the base11 is set to a range of about 0.4≦h1/t≦1.0, where t is a thickness ofthe base 11, as shown in FIG. 3. While an inclination angle of the taperface 11 b is suitably set according to a size of the package 8, aninclination angle θ within a side cross-sectional surface of the base 11parallel to an optical axis is set to a range of about 20°≦θ≦60°. On theother hand, when the base 11 is formed to have the curved face 11 chaving a cylindrical surface or the step 11 d, the radius r of thecylindrical surface (see FIG. 5A) or the height h2 and the length L1 ofthe step (see FIG. 5B) are set to ranges of about 0.4≦r/t, L1/t≦1.0, and0.4≦h2/t≦0.7, where t is a thickness of the base 11.

[0047] The optical fiber 7 may be directly fixed with solder Sd, onto asupport member 11 e that is fixed to the base 11, with no metal ferrule7 a employed, as shown in FIGS. 6A and 6B. It is needless to mentionthat the rear end portion E of the base 11 may also be formed into thecurved face 11 c or the step 11 d as shown in FIG. 5A or FIG. 5B. Thesupport member 11 e may be made of nonmetal such as ceramic, forexample. When the optical fiber 7 is fixed onto the support member 11 ewith an adhesive or a synthetic resin, an optical fiber of whichexternal periphery is not metal-coated may also be used.

[0048]FIG. 7 is a longitudinal cross-sectional view of an LD moduleaccording to the second embodiment of the present invention. The LDmodule 15 differs from the conventional LD module, in the shape of itspackage. The LD module 15 is configured as an optical semiconductormodule having a butterfly-type package. As shown in FIG. 7, a snout 108b of a package 108 consists of a first part 108 b ₁ and a second part108 b ₂. The second part 108 b ₂ has a larger diameter then that of thefirst part 108 b ₁, and is positioned between the first part 108 b ₁ anda front wall 108 c of the package 108. These first part 108 b ₁ and thesecond part 108 b ₂ have a longitudinal hole 108 a through them, forguiding the optical fiber 7 to the outside. The longitudinal hole 108 aconsists of a first longitudinal hole 108 a ₁ of the first part 108 b ₁,and a second longitudinal hole 108 a ₂ of the second part 108 b ₂. Thelongitudinal hole 108 a is, concretely, formed such that an upperboundary F_(UI) of the second longitudinal hole 108 a ₂ is locatedhigher than an upper boundary F_(UO) of the first longitudinal hole 108a ₁. As a result, the optical fiber 7, when led to the outside of thepackage 108 through the longitudinal hole 108 a, is prevented from beingbrought into contact with the internal surface of the secondlongitudinal hole 108 a ₂. Therefore, an excessive bending deformationof the optical fiber 7 is suppressed.

[0049] Consequently, in the LD module 15, in the mounting step of thebase 11 into the package 108, it is possible not only to maintain astate of a large bending curvature radius of the optical fiber 7 by thetaper 11 b but also to prevent the optical fiber 7 from being broughtinto contact with the internal surface of the second longitudinal hole108 a ₂ of the second part 108 b ₂ of the snout 108 _(b), as shown inFIG. 8. Consequently, in the LD module 15, it possible to prevent anexcessive bending deformation of the optical fiber 7 arising from theinterference between the optical fiber 7 and the internal surface of thelongitudinal hole 108 a that would otherwise occur at a portion Aencircled by a dashed line.

[0050] The LD module 15 according to the second embodiment has an effectthat the second part 108 b ₂ provided in the snout 108 b prevents theoptical fiber 7 from being excessively bent, in addition to the effectthat the taper 11 b of the base 11 facilitates the mounting of the base11 into the package 108. Therefore, in the LD module 15, it is possibleto suppress a breakage of the metal-coated optical fiber 7 in themounting step more surely than in the LD module 10 according to thefirst embodiment. Note that the longitudinal hole 108 a may have aplurality of diameters so as to have three or more steps. The snout 108b may take a shape other than that shown in FIG. 7, as far as it ispossible to suppress the bending deformation of the optical fiber 7 inthe mounting step. For example, the second part 108 b ₂ of the snout 8 bis inclined toward the upper end portion of the front wall 108 c, andthe upper boundary F_(UI) of the longitudinal hole 108 a is positionedhigher than the upper boundary F_(UO).

[0051] A package 208 may be used in place of the package 108 (see FIG.9). The package 208 has a front wall 208 c, a rear wall 208 d, a bottomplate 208 e, and a snout 208 b. An external diameter of the snout 208 bis uniform along the longitudinal direction. The snout 208 b has alongitudinal hole 208 a whose diameter is linearly small toward theoutside. In other words, the longitudinal hole 208 a has taper at itsinternal surface along the longitudinal direction. The taper may notnecessarily be formed over the entire of the internal surface along itslongitudinal direction but may be formed at least on a part thereof. Forexample, the taper is formed on only a part of the internal surface nearthe front wall 208 c.

[0052] Further, a package 308 may be used in place of the package 108(see FIG. 10). The package 308 has a front wall 308 c, a rear wall 308d, a bottom plate 308 e, and a snout 308 b having a longitudinal hole308 a. The snout 308 b has a first part 308 b ₁ and a second part 308 b₂. A part of the longitudinal hole 308 a on the first part 308 b ₁ has auniform diameter along the longitudinal direction, and a part oflongitudinal hole 308 a on the second part 308 b ₂ has diameter that islinearly small toward the first part 308 b ₁. External diameters of thesnout 308 b are values corresponding to the diameters of thelongitudinal hole 308 a of the first part 308 b ₁ and of the second part308 b ₂.

[0053] Further, a package 408 may be used in place of the package 108(see FIG. 11). The package 408 has a front wall 408 c, a rear wall 408d, a bottom plate 408 e, and a snout 408 b having a longitudinal hole408 a. The external diameter of snout 408 b and the diameter of thelongitudinal hole 408 a are linearly small from the front wall 408 ctoward the outside of the package 408.

[0054] Furthermore, a package 508 may be used in place of the package108 (see FIG. 12). The package 508 has a front wall 508 c, a rear wall508 d, a bottom plate 508 e, and a snout 508 b having a longitudinalhole 508 a. The external and internal faces of snout 508 b are curvedsuch that an external diameter of the snout 508 b and a diameter of thelongitudinal hole 508 a become gradually small from the front wall 508 ctoward the outside of the package 508.

[0055]FIG. 13 is a longitudinal cross-sectional view of a PD moduleaccording to a third embodiment of the present invention. The PD modulediffers from the LD module shown in FIG. 1, in that the base 11 havingthe tapered rear end portion E is used for the PD module. The PD module20 is an optical semiconductor module having a butterfly-type package. Acarrier 5 on which a PD element 4 is provided and a metal support member11 e are mounted on the base 11. The metal support member 11 e is fixedonto the base 11 with solder. The support member 11 e may be made ofnonmetal, such as ceramic, for example. The optical fiber 7 coated withmetal is directly fixed onto the metal support member 11 e with solderSd, as shown in FIGS. 13, 14A, and 14B. A portion between the opticalfiber 7 and the internal wall of the snout 8 b is hermetically sealedwith a sealant S like solder or synthetic resin. An upper portion of thepackage 8 is sealed with a lid 9.

[0056] The base 11 has the rear end portion E with the tapered face 11b, like that shown in FIG. 1. The PD module 20 is formed as explainedabove. Therefore, as shown in FIG. 15, in the mounting step of the base11 into the package 8, it is possible to prevent an interference betweenthe base 11 and the rear wall 8 d of the package 8. Accordingly, thebase 11 can be easily mounted into the package 8. Consequently, in themounting step, there occurs no misalignment between the PD element 4 andthe optical fiber 7. As a result, it becomes possible to avoid areduction in the optical coupling efficiency between the PD element 4and the optical fiber 7.

[0057] Since the rear end portion E of the base 11 has a taper, theoptical fiber 7 is free from excessive bending at a portion A encircledby a dashed line in FIG. 15 when mounting the base 11 into the package 8with the optical fiber 7 being inserted through the longitudinal hole 8a. Since the optical fiber 7 maintains a state of a large bendingcurvature radius, a breakage of the optical fiber 7 is avoided.

[0058] The rear end portion E of the base 11 may be formed into variousshapes, such as, for example, the curved face 11 c or the step 11 d asshown in FIG. 5A or FIG. 5B.

[0059]FIG. 16 is a longitudinal cross-sectional view of a package of aLD module according to a fourth embodiment. The LD module 30 differsfrom the LD module 10 according to the first embodiment in the type ofpackage. Concretely, in the LD module 30, a package 608 closed with alid 609 is a DIL-type. FIG. 17 is a top plan view of the package of theLD module 30.

[0060] As shown in FIGS. 16 and 17, the LD module 30 has a plurality ofleads Ld extending downward from the side surfaces of the package 608.An unillustrated snout of the package 608 is covered with a rubbercovering B_(g), and a part of the optical fiber 7 that is led out of thepackage 608 is protected by a protective tube T_(g). The package 608 hasa length L not larger than 16 millimeter, a width W not larger than 10millimeter, and a height H not larger than 8 millimeter. The base 11shown in one of FIG. 3 and FIGS. 5A to 6B is mounted into the package 8.

[0061] Therefore, although the LD module 30 is very small, the base 11can be easily mounted into the package 608. Consequently, it is possibleto avoid a reduction in the coupling efficiency between the laser beamemitted from the LD element 1 to the optical fiber 7.

[0062] Since a rear end portion E of the base 11 is formed into thetaper 11 b, a curved face 11 c, or a step 11 d, the optical fiber 7 isnot excessively bent in the mounting step. As a result, the opticalfiber 7 can be maintained at a large bending curvature radius, and thusfree from breakage in the mounting step.

[0063] Note that if a longitudinal hole through which the optical fiber7 passes is formed to have a larger size at the inside than at theoutside of the package 608 as shown in FIGS. 7 to 12, it is possible tomore surely suppress an excessive bending deformation of the opticalfiber 7 in the mounting step, thereby to surely avoid a breakage of theoptical fiber 7.

[0064]FIG. 18 is a longitudinal cross-sectional view of a LD moduleaccording to a fifth embodiment of the present invention. The LD module35 differs from the optical semiconductor modules according to the firstthrough the fourth embodiments, in a base and a lid of a package. In thefirst through the fourth embodiment, the rear end portion of the base 11or a longitudinal hole 708 a provided in the snout 708 b of a package708 was processed in various ways. On the other hand, in the LD module35, a butterfly-type or DIL-type package 708 fails to have a rear wallat a side opposite to the snout 708 b, or it has a rear wall with atleast a part thereof removed.

[0065] For example, in the LD module 35 shown in FIG. 18, thebutterfly-type or DIL-type package 708 has no rear wall opposite to afront wall 708 c. Instead, the wall that faces the front wall 708 c isreplaced by a perpendicular plate 709 a that is integrated with a lid709.

[0066] Therefore, as shown in FIG. 19, the package 708 is open at therear side thereof (i.e., at the left side in FIG. 18 and FIG. 19) whenmounting the base 11 onto the bottom plate 708 e. Hence, it is possibleto insert the base 11 into the package 708 from the left without causinginterference of the optical fiber 7 with the inner wall of thelongitudinal hole 708 a at its end exposed on the front wall 708 c. Itis substantially unnecessary to curve the optical fiber 7 at a portion Aof the package 708 encircled by a dashed line. Since the optical fiber 7can be maintained at a large bending curvature radius, a breakage of theoptical fiber 7 is avoided. Further, it becomes possible to avoid areduction in the optical coupling efficiency between the LD element 1and the optical fiber 7.

[0067] Another package and lid in place of the package 708 and the lid709 may be used if the package is open at the side opposite to the snoutbefore closing with the lid. For example, as shown in FIG. 20, a package808 in place of the package 708 may be used for an LD module 45, whereinthe upper portion of a rear wall 808 d opposite to a front wall 808 c isremoved, and a perpendicular plate 809 b provided integrally with thelid 809 may be located at this removed portion.

[0068] Since the optical fiber 7 can be inserted horizontally in thisembodiment, a snout may be formed to have a longitudinal hole 908 a witha diameter that is uniform in the longitudinal direction, as shown inFIG. 21.

[0069] These LD modules shown in FIGS. 20 and 21 make the mounting stepeasy, without substantially bending the optical fiber 7, in a similarmanner to that shown in FIG. 19. Further, the rear end portion E of thebase 11 may have a taper, a curved face or a step, like that shown inFIG. 3, FIG. 5A, or FIG. 5B, whereby it is possible to prevent theoptical fiber 7 from being excessively bent due to the interferencebetween the rear end portion E of the base 11 and the residual rear wall808 d, in the mounting step.

[0070] In addition, a snout of the package may have forms other thanthose shown in FIGS. 18 and 21. For example, LD modules 65, 75, and 85shown in FIGS. 22A to 22C have packages 1008, 1108, and 1208,respectively. A snout 1008 b of the package 1008 shown in FIG. 22Acorresponds to the snout 208 b shown in FIG. 9, a snout 1108 b of thepackage 1108 shown in FIG. 22B corresponds to the snout 308 b shown inFIG. 10, and a snout 1208 b of the package 1208 shown in FIG. 22Ccorresponds to the snout 408 b shown in FIG. 11.

[0071] These package may be used for not only the LD module but also thePD module according to the third embodiment.

[0072] Advantages derived from the present invention may include one ormore of the following.

[0073] According to one or more embodiment of the present invention, itis easy to mount the base into the package.

[0074] According to one or more embodiment of the present invention, itis possible to avoid a reduction in the coupling efficiency between theoptical fiber and the optical semiconductor element.

[0075] According to one or more embodiment of the present invention, itis possible to prevent the optical fiber from being excessively bent,thereby to maintain the state of a large radius of bending curvature andprevent a breakage of the optical fiber.

[0076] Although the invention has been described with respect to aspecific embodiment for a complete and clear disclosure, the appendedclaims are not to be thus limited but are to be construed as embodyingall modifications and alternative constructions that may occur to oneskilled in the art which fairly fall within the basic teaching hereinset forth.

What is claimed is:
 1. An optical semiconductor module, comprising: anoptical semiconductor element; an optical fiber optically coupled withthe semiconductor element; a base having an upper surface and a lowersurface, the optical fiber and the optical semiconductor element beingmounted on the upper surface; and a package having a bottom plate onwhich the base is directly mounted, a front wall having a hole throughwhich the optical fiber is inserted, and a rear wall opposite to thefront wall, wherein the base has a rear face formed on an end portionopposite to the front wall, the rear face being positioned above thelower surface.
 2. The optical semiconductor module according to claim 1,wherein the rear face is tapered such that the rear face approaches tothe upper surface as approaching to the rear wall of the package.
 3. Theoptical semiconductor module according to claim 1, wherein the rear faceis curved such that the rear face approaches to the upper surface asapproaching to the rear wall of the package.
 4. The opticalsemiconductor module according to claim 1, wherein the rear faceconstitutes a step.
 5. The optical semiconductor module according toclaim 1, wherein a diameter of the hole in the front wall is larger thana diameter of the hole at a position away from the front wall.
 6. Theoptical semiconductor module according to claim 1, wherein the packageis any one of a butterfly package and a dual-in-line package.
 7. Theoptical semiconductor module according to claim 1, wherein at least oneof sides of a main body of the package has a length not larger than 16millimeter.
 8. An optical semiconductor module, comprising: an opticalsemiconductor element; an optical fiber optically coupled with thesemiconductor element; a base having an upper surface and a lowersurface, the optical fiber and the optical semiconductor element beingmounted on the upper surface; a package having a bottom plate on whichthe base is directly mounted, and a front wall having a hole throughwhich the optical fiber is inserted; and a lid having a first portiondisposed above the base and a second portion facing the hole, the firstportion and the second portion of the lid being combined with each otherto cover the package.
 9. The optical semiconductor module according toclaim 8, wherein the package further has a rear wall opposite to thefront wall, the rear wall being combined with the second portion of thelid.
 10. The optical semiconductor module according to claim 9, whereinthe base has a rear face formed on an end portion opposite to the frontwall, the rear face being positioned above the lower surface.
 11. Theoptical semiconductor module according to claim 8, wherein the rear faceis tapered such that the rear face approaches to the upper surface asapproaching to the rear wall of the package.
 12. The opticalsemiconductor module according to claim 8, wherein the rear face iscurved such that the rear face approaches to the upper surface asapproaching to the rear wall of the package.
 13. The opticalsemiconductor module according to claim 8, wherein the rear faceconstitutes a step.
 14. The optical semiconductor module according toclaim 8, wherein a diameter of the hole in the front wall is larger thana diameter of the hole at a position away from the front wall.
 15. Theoptical semiconductor module according to claim 8, wherein the packageis any one of a butterfly package and a dual-in-line package.
 16. Theoptical semiconductor module according to claim 8, wherein at least oneof sides of a main body of the package has a length not larger than 16millimeter.
 17. An optical semiconductor module, comprising: an opticalsemiconductor element; an optical fiber optically coupled with thesemiconductor element; a base having an upper surface and a lowersurface, the optical fiber and the optical semiconductor element beingmounted on the upper surface; a package having a bottom plate on whichthe base is mounted, and a front wall having a hole through which theoptical fiber is inserted; and a lid having a cover portion disposedabove the base, wherein at least one of the base and the package has ameans for preventing any one of a reduction in an optical couplingefficiency between the optical fiber and the semiconductor element; anda breakage of the optical fiber during assembling the semiconductormodule.
 18. The optical semiconductor module according to claim 17,wherein the means includes any one of a rear face that is formed on anend portion opposite to the front wall such that the rear face ispositioned above the lower surface; and a wall portion facing the hole,and combined with the cover portion to cover the package.